Spherical curing agent for epoxy resin, curing agent masterbatch for epoxy resin and their preparation

ABSTRACT

A curing agent for epoxy resins is prepared from an amine and an epoxy, as well as subsequent modification by a polyisocyanate compound, in such a manner that the curing agent is in the form of small spherical particles. The particles can be as small as 0.1 microns. This curing agent can be easily dispersed in curing agent masterbatches and curable compositions with minimal effect on their storage stability. The resulting curable compositions have a wide range of applications, including automobile and electronic adhesives.

This is a continuation of application Ser. No. 706,131, filed May 28,1991, now abandoned.

TECHNICAL FIELD

The present invention relates to a curing agent for epoxy resin and amethod for the preparation of the same.

The present invention also relates to heat curable compositions whichcomprise such curing agents.

The present invention also relates to a curing agent masterbatch forepoxy resin and a method for the preparation of the same. Morespecifically, it relates to a curing agent masterbatch for epoxy resinwhich not only has excellent storage stability and excellentcompatibility with an epoxy resin but also can give a one-componentcuring composition having a low viscosity, a fast curing rate andexcellent storage stability when added to an epoxy resin.

BACKGROUND

Because cured articles prepared from an epoxy resin have excellentadhesion, mechanical properties, thermal properties, chemical resistanceand excellent electrical properties, they are utilized widely andcommercially as paints, adhesives, and electrical and electronicinsulation materials. Epoxy resin formulations used for suchapplications can be either a one-component system or a two-componentsystem.

The two-component system is made of an epoxy resin composition and acuring agent which are separately stored. When needed, they are weighedand mixed just prior to use. In so doing, it is often difficult to avoidmistakes in weighing the correct amount of epoxy and curing agent, aswell as difficult to form a homogeneous curing composition. Thesemistakes are further compounded by the fact the reaction of the epoxyresin and the curing agent starts as they are mixed.

The epoxy resin/curing agent composition is typically in liquid form.The viscosity of the system increases gradually, goes through gelation,and finally the system cures. The time from formulation until it can nolonger be used is called "pot life".

The pot life is decided by the chemical structures and the ratio of theepoxy resin and the curing agent employed. Generally, the system with afaster curing rate has a shorter pot life. If a curing agent which isdesigned with an emphasis on the curing rate is used, a formula canusually be cured at room temperature or lower. However, it willnaturally shorten the pot life and it creates a need to frequentlyformulate a small amount of the composition. Thus, such room temperaturecuring compositions cause a reduction in working efficiency.

In contrast, because a curing agent is added ahead of time in the epoxyresin of the one-component system, the above-mentioned problemsassociated with the two-component system can be eliminated. The curingagent used in such systems is typically called a "latent curing agent".The simplest one-component system is based on the curing agent which cancure epoxy resin at high temperatures. Such agents include, but are notlimited to, dicyandiamide, phenol novolak, adipic dihydrazide, diallylmelamine, diamino maleonitrile, BF₃ -amine complexes, amine salts, andmodified imidazole compounds and the like. Because these curing agentsrequire a high temperature a slow curing rate is inherent. Thus, thereaction proceeds slowly at room temperature and the epoxy resincompound formulated with curing agents can be stably stored at roomtemperature or lower temperatures for a certain period. Thus, thesesystems are especially suitable for one-component systems which arecured at high temperatures.

Such high temperature curing agents do not dissolve in an epoxy resin atroom temperature. If such a curing agent is dispersed as particles, thestorage stability can be improved drastically. This is due to the smallcontact area with the epoxy resin. In this case, a small particle sizefor the curing agent is important because smaller particle sizesincrease the curing rate and also make the structure of the curedarticle very uniform. See J. Appl. Polymer Sci, 32, 5095(1986) Such adispersion type curing agent can also be called a latent curing agent.

Generally, the epoxy resin curing composition of a one-component system,in its normal state, requires a latent curing agent which can beactivated by some form of stimulation. Examples of such latent curingagents include amineimide compounds which are activated by thermaldecomposition; ketimine compounds which are activated by contact withmoisture; aromatic diazonium salt compound, diallyliodonium saltcompounds which are activated by exposure to light; and curing agentswhich are microencapsulated in material which can be destroyed bymechanical pressure or by heat. However, due to problems such asperformance and cost, they are not widely used. As a link before theybecome truly useful, currently the above-described latent curing agentof the dispersion type is important because the preparation methodinvolved is simpler and less expensive.

However, a particularly promising latent curing agent is the modifiedamine curing agent adduct obtained by reaction with an epoxy compound.Due to the modification by the epoxy compound, the flaws of aminecuring, such as volatility which causes problems in handling,hygroscopicity which significantly affects curability, and compatibilitywith the epoxy resin, can be improved. Even further, control of themelting point is also possible. Epoxy resin is cured by polyadditionreaction with a curing agent or by ionic polymerization.

However, because curing agents which require secondary processing tendto be expensive, a curing agent of a catalytic polymerization type whichdoes not depend on the addition of equivalent amounts and can be curedwith the addition of a small amount, will be an advantage. From theaspect of performance, the curing agent of the anionic polymerizationtype which does not risk corrosion of metal (tertiary amine adduct) ispreferred. A suitable catalyst for this purpose is an imidazole/epoxyresin adduct, and its technology is disclosed in detail in JapanesePatent Publication (Kokai) No. SHO 58-13623 (1983) and SHO 61-268721(1986). This solid adduct which is synthesized from amine compounds andepoxy resins can be obtained by reacting an amine compound and an epoxyresin in a solvent and then removing the solvent from the system as awhole. Then, it is crushed and pulverized and then sieved to obtainparticles of the curing agent of a desired size. There is a limitationto the degree of crushing and pulverization, and it is extremelydifficult to commercially prepare fine particles having a Stokesdiameter of smaller than about 4 μm.

Because the above-described preparation method is a long and laboriousprocess, it incurs a very high production cost. In addition, due to thelimitation of the particle size of the curing agent formed by crushingand pulverization and also to the pulverized state, there are thefollowing disadvantages:

a. bulky and inconvenient for packaging and shipment,

b. aggregation of the particles require enormous work to disperse theparticles in an epoxy resin when used,

c. increase in viscosity takes place when added to an epoxy resin,

d. a limit ion the degree of improvement on the curing rate by reductionin particle size, and

e. relatively short stable storage period of the formulated curingcomposition.

Although the particles of the amine compound/epoxy compound adduct has avariety of advantageous features as a curing agent, such advantages havenot been used to the full extent with the one component curingcomposition due to the reasons mentioned above.

On the other hand, the curing agents which are more widely used are onesobtained by treating solid particles of an amine compound/epoxy compoundadduct with a polyfunctional isocyanate to improve its latentcurability. See Japanese Patent Publication SHO 64-70523 (1989) and HEI1-113480 (1989). In this case it is presumed that the polyfunctionalisocyanate has been reacted with the particles of the adduct to form anencapsulated film on their surfaces. With this type of latent curingagent which tends to be expensive, it will be advantageous to use anionic polymerization type curing agent which can be cured with a smallamount of addition without regard to the addition of equivalent amounts.From the performance viewpoint, anionic polymerization type curingagents (tertiary amine adducts) which have no risk of corrosion of metalare preferred. The amine compound/epoxy compound adduct can be obtainedfirstly as a lump by removing the solvent from the reaction system afterreacting the amine compound and the epoxy resin in a solvent.Subsequently, it is crushed and pulverized, and then classified and acuring agent of a desired size is removed. Subsequently, the particlesof the amine compound/epoxy compound adduct are dispersed in a liquidepoxy resin, and a polyfunctional isocyanate compound is added andreacted in a heated state to prepare a desired latent curing agent as amasterbatch. In Japanese Patent Publication (Kokai) No. HEI 1-113480(1989), it is assumed that the polyfunctional isocyanate compound addedhas been adsorbed on the particles of the amine compound/epoxy compoundadduct dispersed in an epoxy resin, and that the hydroxyl group thereinand the moisture therein are reacted to form a polyurethane polymer anda polyurea polymer to form an encapsulating film. The latency of theagent is imparted by this thermal fusible film which prevents directcontact of the particles of the adduct with the epoxy resin. Further,the polymer composition of the encapsulating film is controlled by theamount of the moisture contained in the particles of the adduct to allowthe production of the particles of an encapsulated adduct which hasenough solvent resistance against an organic solvent added only in thepresence of a suitable amount of water and can withstand the mechanicalmixing treatment in the compounding step.

The particles of the amine compound/epoxy compound adduct used for theproduction of the above described prior art curing agent masterbatch arein the form of relatively large pulverized particles having an averageStokes diameter of about 3 μm or more. Due to the shape of theseparticles, there are created various following adverse problems whenused as the curing agent masterbatch.

The increase in viscosity is greater when using pulverized particlesthan when using spherical particles. Accordingly, in regards to a curingagent masterbatch, since there is a limit as to the viscosity which canbe handled, the concentration of the curing agent has to be lowered in arelative manner. Therefore, when this curing agent masterbatch is addedto prepare an epoxy resin curing composition, no problem emerges if theepoxy resin to be cured is the same epoxy resin as the dispersing mediumof the curing agent masterbatch. However, if they are different, thedesired properties of epoxy resin to be cured will be diluted by theepoxy used as the dispersing medium. Further, it is not desirable forthe viscosity to increase during formulation since it will lower thedegree of freedom of formulations design. For example, in order to lowerthe thermal expansion coefficient of the epoxy resin, a filler isusually added to the epoxy resin curing composition. However, theaddition of the filler also increases the viscosity of the compositionand accordingly, it is preferred to use a composition having a low aspossible viscosity in order to increase the amount of the filler whichcan be added. For this reason, even if the curing agent of an aminecompound/epoxy compound adduct treated with a polyfunctional isocyanatecompound has various advantages, such advantages are not fully used inthe one-component curing composition.

OBJECTS

It is an object of the invention to provide fine spherical particles ofa curing agent for epoxy resin which avoids the above-describedproblems.

It is another object of the invention to provide a direct and simplermethod for the preparation of the fine spherical particles of the curingagent for epoxy resin, wherein the method omits the step ofpulverization and sieving and gives a controlled particle size of thefine spherical particles of the curing agent ranging from 0.1 μm to 30μm.

Still another object of the present invention is to provide a curingagent masterbatch for epoxy resin, wherein the masterbatch has a lowviscosity, excellent storage stability and compatibility with an epoxyresin such that it gives a one-component curing composition having afast curing rate and excellent compatibility when added to the epoxyresin.

SUMMARY OF THE INVENTION

Fine spherical particles of curing agent for epoxy resin in accordancewith the invention comprise an amine compound/epoxy compound adduct.More specifically, they relate to curing agents for epoxy resin of atype curable by anionic polymerization. The particles are powdery andnot bulky and can be easily dispersed in an epoxy resin with only asmall increase in viscosity. The curable compositions prepared therefromhave excellent storage stability.

In another aspect of the invention a direct method for the preparationof fine spherical particles of a curing agent for epoxy resin comprisesreacting an amine compound with an epoxy compound in the presence of adispersion stabilizer in an organic solvent capable of dissolving bothsaid amine compound and said epoxy compound but incapable of dissolvingthe adduct formed therefrom at elevated temperatures with agitation, andrecovering fine spherical particles formed from the reaction mixturesolution.

In yet another aspect of the invention a heat curable compositioncomprises, as its major components, an epoxy compound and sphericalparticles of a curing agent for the epoxy compound which are an aminecompound/epoxy compound adduct, said particles having a melting point ofat least 50° C. and a particle diameter of 0.1 μm to 30 μm.

As yet another aspect of the invention a heat curable compositioncomprises, as its major components, an epoxy compound and a hightemperature curable curing agent and, an accelerator comprisingspherical particles of an epoxy curing agent which is an aminecompound/epoxy compound adduct, said particles having a melting point ofat least 50° C. and a particle diameter of 0.1 μm to 30 μm.

The present invention also includes a curing agent masterbatch for epoxyresin wherein the masterbatch comprises a liquid epoxy resin in whichare uniformly dispersed fine spherical particles of an aminecompound/epoxy compound adduct having a melting point of at least 50° C.and a particle diameter of 0.1 μm to 30 μm, wherein said sphericalparticles have been reacted with 1 to 100 parts by weight of apolyfunctional isocyanate compound based on 100 parts by weight of saidparticles.

The present invention further includes a method for preparing of acuring agent masterbatch for epoxy resin with comprises the steps of:

(a) dispersing spherical particles of an amine compound/epoxy compoundadduct having a melting point of at least 50° C. and a diameter of 0.1μm to 30 μm in a liquid epoxy resin;

(b) adding 1 to 100 parts by weight of a polyfunctional isocyanatecompound based on 100 parts by weight of a polyfunctional isocyanatecompound based on 100 parts by weight of said spherical particles at atemperature below the melting point of said spherical particles withagitation; and

(c) heating and agitating the resulting mixture at said temperatureuntil the isocyanate groups in said polyfunctional isocyanate compoundhave been completely reacted.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 is an electron micrograph showing the structure of the particlescomprising a 2-methylimidazole/bisphenol A diglycidyl ether adductprepared by the pulverization method of the prior art.

FIG. 2 is an electron micrograph showing the structure of particlescomprising a 2-methylimidazole/bisphenol A diglycidyl ether additionproduct prepared by the method of the present invention.

FIG. 3 is another electron micrograph showing a cross sectional view ofparticles comprising a 2-methylimidazole/bisphenol A diglycidyl etheradduct prepared by the method of the present invention.

FIG. 4 is an electron micrograph of a cross sectional view of theparticles comprising encapsulated 2-methylimidazole/bisphenol Adiglycidyl ether adduct prepared by the method of the present invention.In FIGS. 3 and 4, the particles may appear oval, as opposed tospherical. This deformation was caused by cutting the samples with amicrotome.

FIG. 5 is another election micrograph showing the structure of theparticles comprising a 2-methylimidazole/bisphenol A diglycidyl etheradduct prepared by the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention the amine compounds and the epoxy compoundswhich can be employed as the starting materials for the preparation ofthe spherical curing agent are selected based on the consideration ofthe properties of the adduct as the curing agent. Important aspects areits chemical structure which promotes the curing reaction by anionicpolymerization, its melting point, and its compatibility with the epoxyresin which will be cured in a molten state, its quick curability andits effect of addition (high curing reactivity with a smallest possibleamount of addition). The melting point is defined herein as thetemperature at which the substance starts to melt, as determined by theconventional methods.

While any kind of amine compounds can be used for this invention, theselection thereof will be determined by the kind of epoxy compound to becombined since in this invention the reaction has to be stopped at thestate of addition reaction and polymerization has to be avoided. Whileit is possible to use any kind of amine compounds with monofunctionalepoxy compounds, the amine which can be combined with polyfunctionalepoxy compounds is an amine compound which has only one active hydrogen,i.e., a secondary amino group that contributes to the reaction of theepoxy group. In both cases, it is preferred that the amine, in addition,has at least one tertiary amino group having no active hydrogen sincethe presence of the tertiary amino group is desirable for increasing theconcentration of amino groups which contribute to the curing reaction ofthe adduct, or in other words, to increase the effect of the curingagent.

As will be described below, bifunctional bisphenol A diglycidyl ether isa most commonly employed epoxy compound. The following compounds aresuitable examples of amine compounds which can be combined withbifunctional bisphenol A diglycidyl ether: imidazoles represented by2-methylimidazole and 2,4-dimethylimidazole, peperazines represented byN-methyl piperazine and N-hydroxylethyl-piperazine, anabasinesrepresented by anabasine, pyrazoles represented by3,5-dimethyl-pyrazole, purines represented by tetra-methyl-quanidine orpurine, pyrazoles represented by pyrazole, and triazoles represented by1,2,3-triazole, and the like.

Any kind of epoxy compound can be employed as the other startingmaterial for the adduct. Examples of such epoxy compounds aremonofunctional epoxy compounds such as n-butyl glycidyl ether, styreneoxide and phenylglycidyl ether, bifunctional epoxy compounds such asbisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol Sdiglycidyl ether and diglycidyl phthalate; trifunctional compounds suchas triglycidyl isocyanurate, triglycidyl p-aminophenol; tetrafunctionalcompounds such as tetraglycidyl m-xylene diamine andtetraglycidyldiaminodiphenylmethane; and compounds having morefunctional groups such as cresol novolac polyglycidyl ether, phenolnovolac polyglycidyl ether and so on. The selection of epoxy is alsodetermined by the type of the amine compound to be combined. Thus, whilethe amine compounds having only one active hydrogen can be combined withany kind of epoxy compounds, monofunctional epoxy compounds alone can becombined with the amine compounds having two or more active hydrogens.

The epoxy compounds are also selected by considering the melting pointof the adduct formed and the compatibility in a molten state withrespect to the epoxy resin which is to be cured. Since the majority ofthe epoxy resins to be cured comprise bisphenol A diglycidyl ether, thiscompound is most typically used as the starting material for thepreparation of an adduct. These bisphenols possess advantageouscompatibility and cost savings.

With an epoxy compound, the concentration of epoxy groups is expressedby "epoxy equivalent weight (EEW)". Lower epoxy equivalent weights givehigher concentration of epoxy groups. However, higher concentrations ofepoxy groups are desirable for the prevention of the decrease ofconcentration of tertiary nitrogen atoms in the adduct. Thus a lowestpossible epoxy equivalent weight is desirable for the epoxy compound.Epoxy compounds having an epoxy equivalent weight of, at most, 1,000,and preferably at most 500 are typically employed.

The melting point of the amine compound/epoxy compound adduct isinfluenced by the chemical structures of the amine compound and theepoxy resin employed, the method of addition, the structure of theadducts formed, and the ratio of the addition of the epoxy resin to theamine compound. With a proper selection of theses factors, the synthesisof desired adducts having a low melting point to a high melting point ispossible. While higher melting points will make the reaction systemeasier to handle, they will also raise the curing reaction-onsettemperature of the reaction mixture. Therefore, from the viewpoint ofcurability, lower melting points are preferred. However, if workability,particularly the workability during summer season, is taken intoconsideration, the melting point has to be at least 50° C.

It is also important to select a solvent which can dissolve the aminecompounds and the epoxy compound as the starting materials but canprecipitate the adduct in the form of particles without dissolution.Generally, a substance can dissolve in a solvent having a similarpolarity. The level of the polarity of a solvent or a substance is oftenexpressed by a solubility parameter having units (cal/cm³)^(1/2). Atypical range of solubility parameters of epoxy compounds will be 8 to11 (cal/cm³)^(1/2), and that of amine compounds will be 8 or greater,and that of the amine compound/epoxy compound adduct will be 11 to 16.Thus, in order to achieve the desired precipitation reaction of thepresent invention, it is suitable to use a solvent having a solubilityparameter of 8 to 11.

Examples of such solvents that can be used in the present invention aremethyl isobutyl ketone, methyl isopropyl ketone, methyl ethyl ketone,acetone, acetic acid, n-butylacetate, isobutyl acetate, ethyl acetate,methyl acetate, tetrahydrofuran, 1,4-dioxane, cellosolve, ethyleneglycolmonoethyl ether, diethyleneglycol dimethyl ether, anisole, toluene,p-xylene, benzene, methylene chloride, chloroform, trichloroethylene,chlorobenzene and pyridine. These solvents can be used alone, or two ormore solvents can be used together. It is possible to use the solventshaving a solubility parameter outside the range of 8 to 11 if two ormore solvents are combined to bring the solubility parameter within theabove-described specified range. However, since the precise solubilityparameter of the solvents to be used may differ naturally depending onthe chemical structures of the amine compound and the epoxy compound, itis essential to make a precise selection for each individual situation.If selection is not precise, even when the precipitation reaction maysmoothly proceed, it may also increase the solubility of the adductformed in the solvent and thus may lower the yield.

The dispersion stabilizer creates a stable dispersion of the adductparticles which precipitate in the solvent during the precipitationreaction. Without such a dispersion stabilizer, the particles of theadduct formed may aggregate and precipitate out as a viscous mass duringthe reaction, and thus the desired fine spherical particles cannot beobtained. Polymeric compounds having affinity to both the organicsolvent and the adduct formed are suitable as the dispersion stabilizerfor this invention. Any graft copolymers, block copolymers, randomcopolymers, and other polymers are suitable. Specific examples ofsuitable graft copolymers are methyl methacrylate/methacrylic acidcopolymers, methyl methacrylate/2-hydroxyethyl methacrylate copolymers,poly(2-hydroxy methacrylate), poly(2,3-dihydroxypropyl methacrylate),poly(acrylamide-2-methylpropanesulfonic acid), poly(vinyl alcohol),poly(vinyl acetate), poly(methacrylic acid), and polyacrylamide,poly(ethylene oxide) and poly(4-vinylethyl pyridium bromide) graftcopolymerized with styrene; methyl methacrylate/methacrylic acidcopolymers, glycidyl methacrylate/styrene copolymers and methylmethacrylate/fluoroaklyl acrylate copolymers graft-copolymerized withmethyl methacrylate; polybutadiene and methyl methacrylate/glycidylmethacrylate copolymers graft-copolymerized with methacrylic acids;polymethyl methacrylate and 2-hydroxyethyl methacrylate copolymers,graft-copolymerized with N-methylol acrylamide; poly(methylmethacrylate), ethyl acrylate/methacrylic acid copolymers methylacrylate/methacrylic acid copolymers, and styrene/methacrylic acidcopolymers graft-copolymerized with 12-hydroxy stearic acid; poly(methylmethacrylate) which is graft-copolymerized with 2-hydroxyethylmethacrylate, and poly(vinyl chloride) graft-copolymerized withethyleneoxide and the like.

Examples of suitable block copolymers are poly(laurylmethacrylate)/poly(methacrylic acid) block copolymers,poly(styrene)/poly(methacrylic acid) block copolymers, poly(ethyleneoxide)/polystyrene/poly(ethylene oxide) block copolymers, andpoly(12-hydroxystearic acid)/poly(ethyleneglycol)/poly(12-hydroxystearic acid).

Examples of suitable random copolymers are vinyl acetate/vinyl alcoholcopolymers, vinyl acetate/N-vinyl pyrrolidone copolymers andN-vinylpyrrolidone/methyl methacrylate copolymers. Examples of otherpolymers are cationized amine-modified polyesters. Dispersionstabilizers having higher molecular weight will increase thestabilization effect. However, if the molecular weight exceeds a certainlimit, it will enhance aggregation of the particles. Thus a suitablemolecular weight range of the dispersion stabilizer in the presentinvention is from 1,000 to 300,000, preferably from 2,000 to 100,000. Avariety of the compounds as described above can be employed as thedispersion stabilizer. However, their effect will differ with thechemical structures of the amine compounds and the epoxy compoundsselected, Thus, their selection will depend on the effects desired andto a large extent involves selection by conventional trial and errortechniques.

The selected amine compound and epoxy compound are dissolved in theselected solvent. After the selected dispersion stabilizer is dissolvedinto this solution, the solution is then heat agitated. The originallyclear solution will become opaque when the adduct is formed. As thereaction progresses, the opaqueness of the reaction system graduallyincreases, with a characteristic milky white turbid dispersioneventually occurring. Then, the following two procedures may beperformed to obtain the desired spherical particles.

According to the first procedure, the reaction is stopped at anappropriate point, i.e., the optimal reaction time for obtaining thehighest yield and avoiding the occurrence of flocculation, by coolingthe reaction system to room temperature. In certain instances a 100%yield will not be possible because flocculation of the particles occursbefore 100% conversion is obtained. In those instances, the appropriatepoint for stopping the reaction is before flocculation occurs. Particlesare separated by filtering the dispersion of the particles of the aminecompound/epoxy compound adduct. After fresh solvent is used to wash offunreacted starting material adhered to the particles, the particles arethen dried to give the desired fine spherical particles of the curingagent.

According to the second procedure, the reaction is continued to aconversion of 100% and then, the reaction system is cooled to roomtemperature and spray-dried to give fine substantially sphericalparticles of a curing agent.

The particle size of the adduct is determined by the types of thestarting materials employed, the reaction conditions selected and thetype and amount of the dispersion stabilizer employed. Of these factors,the type of the dispersion stabilizer selected is an important factor.For example, in the precipitation reaction of 2-methylimidazole andbisphenol A diglycidyl ether in methyl isobutyl ketone, dispersionstabilizer comprising a methyl methacrylate/methacrylic acid copolymergraft-copolymerized with styrene or methyl methacrylate will give aparticle having a particle size of about one micron. On the other hand,a cationized amine-modified polyester will give fine spherical particleshaving a particle diameter of less than one micron, i.e. sub-micron.

Another factor which can have a significant effect is the reactionconditions employed. Generally, the particle size of the adductincreases with increased concentrations of the starting materials andconversions but decreases with increased concentrations of thedispersion stabilizer and reaction temperatures. These tendencies arealso affected by the chemical structure of the specific dispersionstabilizer employed.

In order to obtain a stable dispersion the amount of the dispersionstabilizer employed is typically 5 to 40% by weight, based on the totalweight of the amine compound and the epoxy compound. When the reactiontemperature and the concentration of the starting materials are toohigh, aggregates may easily form even in the presence of a suitableamount of the dispersion stabilizer. Thus, the reaction temperaturewhich can be employed in the present invention is typically 40° C. to90° C., preferably 50° C. to 70° C., and the concentration of thestarting materials, i.e. the amine compound and the epoxy compound, istypically 2 to 40% by weight, preferably 5 to 30% by weight.

Further, the formation of aggregates relates to the agitation conductionand whether the amine/epoxy react completely, i.e. 100% conversion. Anoptimal agitation rate will vary depending on the composition of thestarting materials, the reaction conditions and the configuration of anagitation wing. However, an excessively fast agitation will enhance theformation of aggregates, while excessively slow agitation is notsuitable for the production of fine spherical particles. Thus, theagitation rate will vary for each individual reaction system and thuswill largely be determined by conventional trial and error techniques.Although it may depend also on the reaction conditions, aggregates areusually more easily formed at higher conversions.

Basically, the ratio of the amine compound to the epoxy compound is setin such a way that the concentration of active hydrogens in the aminecompound and the concentration of epoxy groups in the epoxy compound areat an equivalent ratio. However if the system is such that conversiondoes not reach 100%, it is not necessary to use an equivalent ratio, andthe starting materials recovered from the reaction system can be reused.When the filtrate and the washing solution are combined and theconcentrations of the amine compound, the epoxy compounds and thedispersion stabilizer are accurately measured and then extra solvent isremoved and deficient starting materials are supplemented, the result ofthe reaction will be nearly the same as the starting reaction system.Thus, when the starting materials are recovered and recycled, it is alsopossible to use excessive amount of one of the starting materials due tothe relation to the structure of the adduct.

In the present invention it is possible to prepare spherical particlesof the curing agent having a diameter of 0.1 μm to 30 μm. Such particlesare capable of producing a curing agent masterbatch having a lowviscosity and a high concentration of the curing agent particles.

Viscosity and hydroxyl amount are important aspects to consider inselecting a liquid epoxy resin as the dispersion medium for theparticles of the amine compound/epoxy compound adduct in preparation ofa curing agent masterbatch. The hydroxy groups react with apolyfunctional isocyanate compound to increase the viscosity of thereaction system, and may lead to gelation. Therefore, the liquid epoxyresin to serve this purpose should at least contain a very low level ofsuch hydroxy groups.

A low viscosity of the dispersion medium allows the particles of theadduct to disperse at higher concentrations. In addition, use of themasterbatch and the curing composition into which the masterbatch isused should be taken into consideration. Because the epoxy resin as thedispersion medium is incorporated into the chemical structure of thecured article, this consideration is self-evident. In case of a highlyheat-resistant composition, the epoxy resin dispersion medium should beselected accordingly. In case of a low metal corrosive composition, theepoxy resin dispersion medium with a low degradable chlorine contentshould be selected.

The curing agent masterbatch can be prepared by treating the adductparticles with a polyfunctional isocyanate compound. Suitablepolyfunctional isocyanate compounds include the mononuclear andpolynuclear species of toluene diisocyanate and methylene diphenyldiisocyanate, hydrogenated methylene diphenyl diisocyanate,1,5-naphthalene diisocyanate, isophorone diisocyanate, hexamethylenediisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate,tetramethylxylene diisocyanate, 1,3,6-hexamethylene triisocyanate,lysine diisocyanate, triphenylethane triisocyanate,TRIS(isocyanateophenyl) thiophosphate, polyfunctional isocyanatecompounds formed by addition of such compounds and other activehydrogen-containing compound, and any mixtures thereof.

The amount of the polyfunctional isocyanate compound employed for theparticles of the adduct affects the storage stability and the curabilityof a curing agent masterbatch. With the same particles of the additionproduct, increased amounts of the polyfunctional isocyanate compoundimprove the storage stability but lower the curability. Thus, for adductparticles having a diameter of 0.1 μm to 30 μm, the polyfunctionalisocyanate compound is employed in an amount of 1 to 100 parts byweight, preferably 10 to 50 parts by weight for sub-micron-sizeparticles and preferably 2 to 10 parts by weight for micron sizeparticles based on 100 parts by weight of the adduct particles. Thus,the compromise between storage stability and curability varies dependingon the size of the adduct particle, with smaller particle sizesrequiring increased amounts of polyfunctional isocyanate compound.

Depending on the application of the adduct particles, it is oftenpreferred to adjust the moisture content of the particles before theiruse. Moisture in the particles can easily be increased by exposure to ahigh humidity.

The particles of the adduct are uniformly dispersed in a liquid epoxyresin. Because fine particles often form secondary particles, it isrequired to mechanically disperse them in the epoxy resin as primaryparticles. For example, by blending with a three roll mill and heatingat a temperature lower than the melting point of the particles withconstant agitation, the adduct particles can be dispersed in the epoxyresin. When the temperature has reached a predetermined temperature, apolyfunctional isocyanate compound is then added at a rate that does notcause excessive increase in temperature to react with the adductparticles. The heating and agitation are continued to reduce theconcentration of the polyfunctional isocyanate compound as much aspossible. The reaction is completed when no free isocyanate groupsremain. However, complete reaction of the isocyanate groups is notalways necessary. By the treatment with this polyfunctional isocyanatecompound, as clearly demonstrated by comparison of the transmissionelectron micrographs as shown in FIGS. 3 and 4, an encapsulating layeras described in Japanese Patent Publication (Kokai) No. HEI 1-113480 isformed on the surface of the particles of the adduct. The encapsulatedparticles as shown in these photographs were those obtained by treatingparticles of a 2-methylimidazole/bisphenol A diglycidyl ether adductwith 20% by weight of poly-MDI (MILLIONATE® MR-300 polyisocyanate fromNippon Polyurethane Kogyo K.K.), based on the weight of the adduct andthe curing agent masterbatch of the encapsulated particles of the adductwere added to a bisphenol A diglycidyl ether/polyamide polyamine curingcomposition, and the mixture was heated to cure at 50° C. for 48 hours.The sample thus prepared was sliced to a thin film by means of amicrotome and then stained with osmic acid.

According to the method of the present invention, the particles of anamine compound/epoxy compound adduct as the curing agent for epoxy resincan be prepared without pulverization and sieving as done inconventional methods. In addition, the formed particles are sphericaland their size can be at the sub-micron level, i.e. 0.1 μm, up to micronlevels of 30 μm. Even further, the latent curability of the resultingparticles is far superior to that of the prior art, because of thepolymeric dispersion stabilizer compound which has high affinity to boththe organic solvent and the adduct.

The spherical form of the particles provides a variety of advantages tothe curing agent itself or the curing composition which is blended withthe curing agent. The advantages are indicated below.

a. Due to high bulk density, the packaging volume can be reduced, thusreducing packaging and shipping costs.

b. Dispersion into an epoxy resin is relatively simple, thus simplifyingthe preparation method of a curing composition.

c. Increase in viscosity after addition to epoxy resin is minimal. Thisis a very desirable feature when the epoxy resin has a relatively highviscosity. This advantage provides a higher degree of freedom forformula design.

d. The improved latent curability provides a curing composition having alonger storage stability.

As evident from the description herein, the present invention can extendthe storage period of time of a one-component curing composition withoutcausing any damage to the curability.

The spherical particles of the curing agent of the present invention, byitself, can function as a latent anionic polymerization type curingagent. When used together with other polyaddition type curing agentswhich are curable at high temperatures, such as dicyandiamide and acidanhydrides, they can work effectively as a latent accelerator toefficiently lower their curing temperature.

As stated above, according to the present invention, a low viscositycuring agent masterbatch can be prepared much more simply than by theconventional methods. Thus, when the viscosity is kept the same, it ispossible to prepare a highly concentrated curing agent masterbatch. Themasterbatch thus prepared, when added to an epoxy resin, can give acuring composition having a remarkably lower viscosity than the oneprepared from pulverized adduct particles. This means that more fillercan be added at the same level of viscosity. The addition of higheramounts of filler not only reduces the cost but also reduces theshrinkage that can occur during curing of the composition. Theelectrical conductivity of the composition can be improved when using anelectrically conductive filler.

The above-mentioned features allow the spherical particles of thepresent invention to be used as a one-component curing composition forepoxy resin for a broad range of applications. Examples are structuraladhesives, such as adhesives for assembly of automobiles, adhesives forassembly of optical equipment; and adhesives for assembly of electronicand electrical equipment; powder paint in the paint field, baking paint,and the like; impregnation of glass cloth for printed circuit board, ICchip sealing material, electrically conductive paint, solder resist,adhesive for die bonding, adhesive for printing board, and electricallyconductive adhesive and the like in the electronic field; impregnatingelectrically insulating material coil, adhesive for battery casing, andadhesive for tape head, and the like in the electrical field.

In order to further illustrate the practice of the present invention andthe advantages thereof, the following examples are provided. However,these examples are in no way meant to be limitative, but merelyillustrative.

COMPARATIVE EXAMPLE 1

Xylene (600 g) and 2-methylimidazole (hereinafter "2 Mz") (300 g) werecharged in a 3,000 ml three-necked round bottom flask equipped with athermometer, a reflux condenser and stainless steel propeller typeagitating device. With constant agitation, the flask was heated at 120°C. to completely dissolve the 2 Mz. Subsequently, while agitation wascontinued, a solution prepared by dissolving 680 g of EPIKOTE® 828bisphenol A diglycidyl ether, (epoxy equivalent weight: 186) a productof Yuka-Shell K.K., in 300 g of xylene was added over a period of 90minutes while the temperature was kept at 120° C. Because the adductformed was insoluble in xylene, it precipitated as a viscous mass as thereaction proceeded. Reaction was continued for additional 2 hours. Afterconfirming that the conversion had exceeded 98% by the analysis ofepoxyl groups by the method to be described in Example 4, thetemperature was lowered to room temperature.

Agitation was stopped, and the xylene in the upper layer was removed bydecantation, and the remaining contents of the flask were heated to 140°C. to remove the remaining xylene by distillation under reduced pressureof 10 mm Hg. Subsequently, the molten adduct was poured in a shallowdish and cooled to obtain a novolak-like reddish brown adduct. Thisproduct was crushed and pulverized repeatedly by a jet mill and finallyfractioned to obtain particles having a Stokes diameter of 2.9 μm. Todetermine Stokes diameter, crushed and pulverized particles weredispersed in cyclohexane by using a table top type SINPAR® VS-10111ultrasonic cleaner, a product of Iuchi Seieido K.K., and measurement wastaken in an automatic particle size distribution CAPA-700 analyzer ofultracentrifuge type, a product of Horiba Seisakusho K.K. The electronmicrograph of the particle's shape is illustrated in FIG. 1.

Curing agent particles made from 2 Mz/epoxy resin adduct prepared by,this prior art method (pulverization method) was added to EPIKOTE® 828epoxy, and the property of the curing composition was determined. Thecuring composition was prepared by the following procedure.

Particles of the 2 Mz/EPIKOTE 828 epoxy adduct 10 parts by weight (10parts per hundred parts resin) were added to 100 parts by weight ofEPIKOTE 828 epoxy, and then blended briefly. The particles of the curingagent were then completely dispersed by a three-roll mill. As is known,the fine particles which are primary particles in a dry state formsecondary particles by aggregation, and enormous mechanical abrasion andcrushing are required for obtaining perfect dispersion. The dispersionwas checked with a grain gauge for each passage through the three-rollmill. When they were passed through the roll mill at a rate of 120g/minute, three passages were required for obtaining a perfectdispersion of the particles of the curing agent.

Viscosity and gel times (measured by the stroke cure method), were usedto measure the curing rate of the curing composition. A cured materialwas prepared separately by curing at 120° C. for 30 minutes, and tensileproperties and water resistance (water absorption when soaked in boilingwater for 6 hours), and Tg were measured as the measure of heatresistance. The results are shown in Table 1.

EXAMPLE 1

Methyl iso-butyl ketone ("MIBK") (2,750 g) was charged in a 5,000 mlthree-necked round-bottom flask equipped with a thermometer, a refluxcondenser and a glass half moon-shaped agitating device, 2 Mz (160 g)was then added to the flask and temperature was raised to 60° C. todissolve the 2 Mz completely. Subsequently, 425 g of a 30 weight % MIBKsolution of a methyl methacrylate/methacrylic acid copolymergraft-copolymerized with GC-10 methyl methacrylate, a product ofToagosei Chemical Ind. Co., Ltd. was added as a dispersion stabilizer.Then 700 g (1.88 equivalent weight) of a 50 weight % MIBK solution ofEPIKOTE® 828 epoxy was added. The concentration of the startingmaterials for the adduct was 12.6% by weight, the total concentration ofall starting materials was 15.8% by weight and the amount of thedispersion stabilizer based on the weight of the starting materials foradduct was 25% by weight. In this Example and those that follow, thesephrases have the following definitions:

"the concentration of the starting materials for the adduct" means thetotal weight of the amine compound and the epoxy compound based on thetotal weight of the amine, the epoxy, the dispersion stabilizer and thesolvent; and

"the total concentration of the starting materials" means the totalweight of the amine, the epoxy and the dispersion stabilizer based onthe total weight of the amine, the epoxy, the dispersion stabilizer andthe solvent.

While the contents were agitated at a rate of 400 r.p.m., the reactionwas carried out at 60° C. for 8 hours. The reaction mixture which wasinitially transparent gradually turned to bluish translucent complexion,and then changed to a milky opaqueness at the end of the reaction. Thereaction mixture was cooled down to room temperature after the reactionwas completed, and left to stand overnight to precipitate the formedparticles. After removing the supernatant by decantation, particles wereseparated by filtration, and then washed thoroughly with MIBK and driedin vacuum at 40° C. for 24 hours to obtain 268 g of white particles of acuring agent. The particle size in the MIBK dispersion immediately aftercompletion of the reaction was measured by a Laser particle analyzer(manufactured by Ohtsuka Denshi K.K., LPA 3000/3100). The averageparticle size was 2.5 μm.

As clearly shown by the example of recovery and reutilization ofunreacted starting materials which will be explained in Example 4, apart of the dispersion stabilizer being used for the formation ofparticles was immobilized on the particles, and thus could not berecovered. Perhaps a portion of the stabilizer had reacted with theepoxy groups and were fixed chemically into the particles, with theremaining portion perhaps immobilized by adsorption. However, if such anamount was determined for the fourth particle growth experiment inExample 4, it was on average 40% of the consumed starting materials forthe adduct. Thus, if 268 g is used as the weight for the particles ofcuring agent obtained in this example, the formed adduct comprises 190 gthereof and the immobilized dispersion stabilizer comprises 78 g.Therefore, the conversion was 37%. If the dispersion stabilizer wasregarded as a starting material for the formed particles, the yield ofparticles will be 42%.

Although the reaction was stopped at a conversion of 37% in thisexample, it was confirmed by a preliminary experiment that furtherprogress of the reaction will cause micro- and then macro-flocculation.The agitation rate, i.e., 400 r.p.m., used in this experiment wasdetermined by the preliminary experiment. With faster agitation rates,e.g. greater than 600 r.p.m., aggregates were formed before theconversion reached 37%, and with slower agitation rates, e.g. less than100 r.p.m., perfectly spherical particles of the adduct will not beformed.

The shape of the particles by electron micrography is shown in FIG. 2,and they are nearly perfect spheres. The bulk density of these particlesis compared with that of the pulverized particles prepared by the methodof the prior art, at the same size, in Table 1. Because sphericalparticles can be packed more compactly, the bulk density was nearlydouble that of the pulverized particles, thus offering a compact packagefor convenient shipment.

The spherical particles of the curing agent thus prepared were added toEPIKOTE® 828 epoxy in the same manner as described in ComparativeExample 1 to prepare a curing composition. But, dispersion of theparticles of the curing agent by a three roll mill is far easier thanobserved in Comparative Example 1. While three passages were required inthe Comparative Example 1, only one passage was required to create aperfectly dispersed state. The properties of the curing composition areshown in Table 1.

Compared to the curing composition containing pulverized curing agentparticles, the characteristic difference is viscosity. While adding evensuch a small amount, such as 10 phr. of pulverized curing agentparticles could raise the viscosity of the EPIKOTE 828 epoxy from 13,800cps to 42,000 cps at 20° C., the viscosity of the spherical curing agentparticles of this Example 1 was increased only to 27,000 cps. Adifference was also seen in gelation rate and storage stability.Although the curing rate of the particles of the curing agent preparedby the method of the prior art is slightly slower than the curing agentof this invention, the pot life of the Comparative Example 1 was only 1week whereas that of the present invention was 8 weeks. Without beingheld to any particular theory, it is believed that the presence of thedispersion stabilizer immobilized on the particles' surface as comparedto the curing agent particles prepared by the method of the prior art,which typically have no dispersion stabilizer immobilized therein,resulted in the difference as described above. There were no particulardifferences in the color, physical properties and water resistance(water absorption) of the cured material.

EXAMPLE 2

MIBK (3,400 g) was charged in the same reactor as in Example 1, and then2 Mz (1.39 epoxy equivalent weight) (115 g) was added, and thetemperature was raised to 50° C. to dissolve the content completely.Subsequently, 146 g of GC-10 dispersion stabilizer (25 weight % methylethyl ketone/butyl acetate solution) was added. Then 500 g of a 50weight % MIBK solution of EPIKOTE® 828 (1.34 epoxy equivalent weight)was added. The concentration of the starting materials for the adductwas 8.8%, the total concentration of the starting materials was 9.7% byweight, the amount of the dispersion stabilizer based on the weight ofthe starting materials of the adduct was 10.0% by weight. They werereacted at 50% for 24 hours with constant agitation. After completion ofthe reaction, the reaction mixture was treated in the same manner asExample 1 to obtain 81 g of white particles of a dried curing agent. Theparticles thus obtained were perfect spheres, and the diameter was 0.21μm. Calculation on the same basis as in Example 1 gave a conversion of16% and a particle yield of 20%.

The bulk density of the particles of the curing agent was drasticallydecreased as shown in Table 1, by as much as the decreased proportion ofsize. However, in the preparation of the curing composition by additionof 10 phr. to EPIKOTE® 828 epoxy, there was no tendency for thedispersed state to decline. Thus a perfectly dispersed state was createdby only one passage through the three-roll mill.

The properties exhibited by the curing compositions of Example 2 are inTable 1, together with those of Example 1 and Comparative Example 1.Compared to Example 1, decrease in particle size has resulted in theincrease in viscosity of the curing composition, and the curing rate hasbeen increased substantially. On the contrary, the storage stability hasdeclined by as much proportion as the increased portion of the curingrate, but the level is still fairly high compared to that of theComparative Example 1. The effect of the decrease in the size of theparticles of the curing agent can be seen in the property of the curedproduct. Although the color of the cured material, like Example 1, wasreddish brown and translucent, improvements, however small, were seen onheat resistance, tensile strength, elongation and water resistance.

EXAMPLE 3

MIBK (2,750 g) was charged in the reactor of the Example 1, and then 195g (1.94 epoxy equivalent weight) of N-methylpiperazine (herein "N-MP")was added and the temperature was raised to 60° C. to dissolve thecontents completely. Subsequently, after adding 425 g of GC-10 as thedispersion stabilizer, 700 g (1.88 epoxy equivalent weight) of a 50%MIBK solution of EPIKOTE® 828 epoxy was added. The concentration of thestarting materials for the adduct was 13.4%, the total concentration ofthe starting materials was 16.5% by weight, the amount of the dispersionstabilizer was 23.4% by weight, based on the weight of the startingmaterials for the adduct. They were reacted at 60° C. for 14 hours withconstant agitation at a rate of 400 r.p.m. After completion of thereaction, the spherical particles of a curing agent formed by theprocedure of Example 1 were recovered as dried white particles. Theamount of the particles was 174 g, the particle size was 0.55 μm and thebulk density was 0.26. The calculation on the same basis as in Example 1gave a conversion of 23% and a particle yield of 26%.

The particles of the curing agent thus obtained was added in 10 phr.dosage to EPIKOTE 828 epoxy in the same manner as in Comparative Example1 to prepare a curing composition. The dispersed state was no moredifferent from Example 1 and Example 2. Thus a perfectly dispersed statewas created by only one passage through a three roll mill. Theproperties of the curing composition are shown in Table 1. Compared tothe curing agent made of the 2 Mz/EPIKOTE 828 epoxy adduct, the curingrate at 120° C. was faster and the curing rate at 140° C. was slower. Onthe other hand, the storage stability was substantially better than thatof the curing agent made of the 2 Mz/EPIKOTE® 828 epoxy.

The properties of the cured material were compared with those of thecuring agent made of the 2 Mz/EPIKOTE 828 epoxy adduct. A majordifference was its external appearance. Unlike the reddish brownsemi-clear material of the latter, the cured material made ofN-MP/EPIKOTE 828 epoxy adduct was a slight yellowish, transparentmaterial and showed slightly inferior tensile strength, but greaterelongation. The heat resistance and water resistance of this curedmaterial were also slightly inferior.

EXAMPLE 4

In Examples 1 to 3, the reaction was stopped at a conversion of lessthan 50%. From a commercial viewpoint, it is preferred to recover andreuse unreacted starting materials. For this matter, it is desirable toquantitatively and accurately determine the concentrations of thestarting materials in the recovered filtrate and washing liquid, removeunnecessary solvent, readjust it to the original reaction composition,and to obtain the particles of the adduct identical to the first run ofthe reaction. If it is possible, it should be possible to convert thestarting materials into the particles of the adduct without any waste byrepeating the process. Such an example is illustrated below.

MIBK (2,750 g) was charged in the reactor of Example 1, and then 2 Mz(160 g) was added to the reactor, and the temperature was raised to 60°C. to dissolve the contents completely. Then, 425 g of GC-10 (30 weight% MIBK solution) was added as the dispersion stabilizer, and then 700 gof a 50 weight % MIBK solution of EPIKOTE® 828 epoxy was added. Theconcentration of all starting materials for the adduct was 12.6% byweight, the total concentration of the starting materials was 15.8% byweight and the amount of the dispersion stabilizer was 25% by weight,based on the weight of the starting materials for the adduct. They werereacted at 60° C. for 8 hours with agitation at a rate of 400 r.p.m.After completion of the reaction the particles formed were recovered bythe procedure of Example 1 to obtain white dried particles.

The filtrate after removal of the particles and the washing liquid:werecombined, and the concentrations of 2 Mz, EPIKOTE 828 epoxy, and thedispersion stabilizer in this combined liquid were measured. Thefollowing methods of measurement were used:

Concentration of 2 Mz in the presence of an epoxy resin: After addingglacial acetic acid and crystal violet to the sample solution, it wastitrated with 0.1 N perchloric acid/acetic acid solution.

Concentration of the epoxy resin in the presence of 2 Mz: the epoxy ringwas cleaved by hydrochloric acid, and excess hydrochloric acid wastitrated potentiometrically with a silver nitrate solution.

Concentration of the dispersion stabilizer: Determined by GPC, from thepeak area ratio, using standard polystyrene as the internal standard andalso 3.32 as the proportionality constant. The relationship between theweight ratio of a dispersion stabilizer (GC-10) to standard polystyreneand the peak area ratio of the dispersion stabilizer is represented bythe following equation:

    (W.sub.GC-10 /W.sub.pst)=3.32 (A.sub.GC-10 /A.sub.pst) wherein W=weight, A=peak area, and pst=standard polystyrene.

The results of the measurements are shown in Table 2, as the % recovery,relative to the amounts of the starting materials. Since the precisionof the measurement was not high, the actual recovery percentage was notclose to theoretical percentages. However, as will be described below,even this level of accuracy can be used for most practical purposes.

The combined filtrate and washing liquid were concentrated to 2,500 g invacuum, and was used for the second run of the reaction. AdditionalEPIKOTE epoxy and GC-10 stabilizer were added to readjust the reactioncomposition to match the one in the first run, and it was reacted for 6hours under the same conditions. Difference of the reaction time fromthe first run was caused by slight difference of the course of thereaction, since there was a tendency to form aggregates in this reactiontime. Third and fourth reaction runs were carried out by the sameprocedure. The results are summarized in Table 2. As the reactionprogresses by repetition, it creates some difference in the course ofthe reaction, but particles of the adduct of the same size are obtainedwithout any problem.

                                      TABLE 1                                     __________________________________________________________________________                      Comparative                                                 Properties        Example 1                                                                             Example 1                                                                             Example 2                                                                             Example 3                           __________________________________________________________________________    Particles of curing agent                                                     Shape             Pulverized                                                                            Spherical                                                                             Spherical                                                                             Spherical                           Particle size (μm)                                                                           2.9     2.5     0.21    0.55                                Bulk density (g/ml)                                                                             0.30    0.62    0.18    0.26                                Number of passage through a three-                                                              3       1       1       1                                   roll mill required for dispersion                                             Curing composition                                                            Viscosity (cps, 20° C.)                                                                  42,000  27,300  40,500  38,000                              Gel time (seconds: 120° C.                                                               90      129     93      81                                  140° C.    62      66      56      78                                  Pot life (days, 20° C.)                                                                  7       56      47      72                                  Cured product                                                                 External appearance                                                                             Reddish brown                                                                         Reddish brown                                                                         Reddish brown                                                                         Pale yellow                                           translucent                                                                           translucent                                                                           translucent                                                                           clear                               Tg (°C.)   156     157     158     146                                 Tensile property: Strength (kg/cm.sup.2)                                                        532     571     622     515                                 % Elongation      2.4     3.2     6.1     8.8                                 Water absorption in boiling water                                                               0.9     0.9     0.7     0.8                                 (%, soaked for 6 hours)                                                       __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                                         First   Second  Third Fourth                                 Results          Run     Run     Run   Run                                    ______________________________________                                        Particles of adduct                                                           Reaction temperature (°C.)                                                              60      60      60    60                                     Reaction temperature (hr)                                                                      8       6       7     5.5                                    Amount of particles formed (g)                                                                 277     260     290   224                                    Conversion (%)   39      36      40    31                                     Yield of particles (%)                                                                         43      41      45    35                                     Particle size (μm)                                                                          2.5     3.3     3.3   3.5                                    Unreacted starting materials                                                  recovered                                                                     2Mz (%)          61.9    72.5    55.8  71.6                                   Epikote 828 (%)  50.9    57.6    43.2  60.3                                   GC-10 (%)        23.6    30.3    37.9  39.2                                   Curability and storage stability                                              Gel time (sec., 120° C.)                                                                126     137     124   133                                    Pot life (days, 20° C.)                                                                 47      52      45    48                                     ______________________________________                                    

In Table 2, the percent recovery of EPIKOTE® 828 epoxy was only about80% of 2 Mz. The amount of charge of 2 Mz was 97%, but this relativepercent recovery was substantially lower. On the other hand, the percentrecovery of the dispersion stabilizer should reach about 100%, if therewas no immobilization on the particles. This evidence clearly suggestsconsumption of a part of the epoxy groups by the dispersion stabilizer,thus causing chemical immobilization of the dispersion stabilizer on theparticles. Other portions of stabilizer were immobilized by adsorption.Attempt was made to calculate the amount of the dispersion stabilizerimmobilized on the particles. Although the data is varied, it reached onaverage about 40% of the formed adduct.

The particles of the adduct obtained by the procedure of Example 1 wereadded in 10 phr. dosage to EPIKOTE 828 epoxy to prepare a curingcomposition. Properties are shown in Table 2, but there are nosignificant differences in curability and storage stability. The aboveresults indicate that there is no problem in recovery of unreactedstarting materials and the recovered materials can be recycled for use.

COMPARATIVE EXAMPLE 2

MIBK (3,400 g) was charged in a 5,000 ml three-necked, round bottomflask equipped with a thermometer, reflux condenser and a halfmoon-shaped glass agitator, and then 2 Mz (115 g) (1.39 epoxy equivalentweight) was added, and the temperature was raised to 50° C. tocompletely dissolve the contents. Then, 146 g of GC-10 (25 weight %) ina methyl ethyl ketone/butyl acetate solution was added as the dispersionstabilizer, and then 500 g (1.34 epoxy equivalent weight) of 50 weight %"BADGE" EPIKOTE® 828 bisphenol A diglycidyl ether, a product ofYuka-Shell K.K., (epoxy equivalent weight: 186) in MIBK solution wasadded. The concentration of the starting materials for the adduct was8.8% by weight, the total concentration of the starting material was9.7% by weight, and the amount of the dispersion stabilizer added, basedon the weight of the starting materials for the adduct was 10.0% byweight. While the contents were agitated at a rate of 400 r.p.m., thereaction was carried out at 50° C. for 24 hours. The reaction system,which was transparent initially gradually changed to bluish translucent,and it finally changed to a milky white opaqueness at the end of thereaction.

After the reaction, the reaction mixture was cooled down to roomtemperature, and left to stand overnight to precipitate the particlesformed. After removing the clear supernatant by decantation, particleswere isolated by filtration and washed thoroughly with MIBK. Then, theparticles were dried under vacuum at 40° C. for 24 hours to obtain 81 gof white particles of the adduct. The average particle size, analyzed bya Model LPA 3000/3100 laser particle size analyzer, manufactured byOhtsuka Denshi K.K. was 0.21 μm. According to the observation with anelectron microscope, the particles of the 2 Mz/EPIKOTE 828 epoxy adductprepared by this precipitation reaction method were spherical. Theanalysis by infrared absorption spectroscopy shows that part of thedispersion stabilizer used has been immobilized on the particles of theadduct.

Forty parts by weight of the spherical particles of the adduct thusprepared were added to 100 parts by weight of BADGE epoxy which hardlycontained hydroxy groups (DER® 332 epoxy, a product of Dow Chemical Co.,(epoxy equivalent weight: 173). The particles were then dispersedcompletely by passing the mixture through a three-roll mill to form acuring agent masterbatch. Then, this curing agent masterbatch was addedto BADGE epoxy having an epoxy equivalent weight of 186 to bring theconcentration of the particles of the adduct to 15% by weight to preparea curing composition. This curing composition was heated and cured at100° C. for one hour and then at 150° C. for 3 hours to prepare a curedproduct, and its glass transition temperature (Tg), tensile propertiesand water absorption were measured. The following methods were used formeasurements:

Tg: measured by a differential calorimeter

Tensile property: measured according to JIS K7113

Water absorption: weight percent gained of a sample having a diameter of39 mm and a thickness of 4 mm after soaking it in water at 100° C. for 6hours.

The properties of the curing agent masterbatch, the curing compositionand the cured product are shown in Table 3.

COMPARATIVE EXAMPLE 3

MIBK (3240 g) was charged into the three-necked round bottom glass ofthe device as described in Comparative Example 2. Then, 2 Mz (115 g) wasadded, and the temperature was raised to 50° C. to dissolve the contentcompletely. Then, after adding GC-10 (219 g), a 50 weight % EPIKOTE® 828epoxy solution in MIBK (500 g) was added. The concentration of thestarting materials for an adduct was 9.0% by weight, the totalconcentration of the starting materials was 10.3% by weight and theamount of dispersion stabilizer added, based on the weight of thestarting materials for the adduct was 15.0%. While the contents wereagitated at 400 r.p.m., the reaction was carried out at 50° C. for 24hours to obtain spherical particles of an adduct having an averageparticle diameter of 0.52 μm (107 g) by the procedure of ComparativeExample 2. A curing agent masterbatch, a curing composition and a curedproduct were prepared by the procedure of Comparative Example 2, andtheir properties were measured. The results are shown in Table 4.

EXAMPLE 5

One hundred and twenty grams of the particles of the 2 Mz/EPIKOTE 828epoxy adduct prepared in Comparative Example 1, was kept undersaturation humidity for 48 hours to absorb 5.2% by weight moisture,based on the adduct. These moisture-regulated particles of the adductwere added to 300 g of DER®332 epoxy, and they were blended briefly andpassed through a three-roll mill for obtaining a complete dispersion.The viscosity of the dispersion at 30° C. was 29,100 cps. Three hundredand fifty grams of the dispersion were transferred to a reactor equippedwith a heatable agitation device and the reactor was heated to 60° C.with constant agitation. While maintaining the reactor at 60° C., 10 gof MR-300 poly-MDI, a product of Nippon Polyurethane Kogyo K.K. wasadded, and the reaction mixture was kept at this temperature for twohours, and then cooled to prepare a curing agent masterbatch. Accordingto the analysis by a Schimadzu FTIR analyzer, 1.8% of poly-MDI remainedunreacted. The viscosity of this curing agent masterbatch at 30° C. was59,500 cps. In the same manner as in Comparative Example 3, thismasterbatch was added to EPIKOTE® 828 epoxy so that its concentration,based on the weight of the adduct, would be 15% by weight to prepare acuring composition. A portion was used to prepare the sample for themeasurement of the properties of the cured product obtained, asdescribed in Comparative Example 3. The properties of the curing agentmasterbatch, the curing composition, and the cured product are shown inTable 3.

EXAMPLE 6

Three hundred and fifty grams of the dispersion of the particles of the2 Mz/EPIKOTE 828 epoxy adduct prepared in the same manner as Example 5was transferred to a reactor equipped with a heatable agitation device.With constant agitation, the temperature was raised to 60° C.Subsequently, while maintaining this temperature, 20 g of MR-300poly-MDI was added over a period of about one hour. This temperature wasmaintained for 2 hours, and then the reaction mixture was cooled toprepare a curing agent masterbatch. This curing agent masterbatchcontained 2.3% of unreacted poly-MDI. The viscosity of this curing agentmasterbatch at 30° C. was 112,000 cps. Subsequently, a curingcomposition was prepared by the procedure of Example 5 and a sample of acured product was prepared by the procedure of Comparative Example 2.Properties of curing agent masterbatch, curing composition and curedproduct are shown in Table 3.

EXAMPLE 7

Three hundred and fifty grams of the dispersion of particles of the 2Mz/EPIKOTE® 828 epoxy adduct prepared in the same manner as Example 5were transferred to a reactor equipped with a heatable agitation device.With constant agitation, it was heated to 60° C. Then, while maintainingthis temperature, 30 g of MR-300 poly-MDI was added over a period ofabout one hour. The temperature was kept at 60° C. for additional 3hours, and then the reaction mixture was cooled to form a curing agentmasterbatch. This curing agent masterbatch contained 1.7% of unreactedpoly-MDI. The viscosity of this curing agent masterbatch at 30° C. was194,000 cps. Subsequently a curing composition was prepared by theprocedure of Example 5 and a sample of a cured product was prepared bythe method as described in Comparative Example 2. The properties of thecuring agent masterbatch, the curing composition and the cured productare shown in Table 3.

EXAMPLE 8

Three hundred and fifty grams of a dispersion of particles of 2Mz/EPIKOTE 828 epoxy adduct prepared in the same manner as Example 5were transferred to a reactor equipped with a heatable agitation deviceand heated to 60° C. with constant agitation. Then, while maintainingthis temperature, 40 g of MR-300 poly-MDI was added over a period forabout one hour, and the mixture was heated at the same temperature foradditional 3 hours, and then cooled to form a curing agent masterbatch.This curing agent masterbatch contained 2.6% of unreacted poly-MDI. Theviscosity of the curing agent masterbatch at 30° C. was 305,000 cps.Subsequently, a curing composition was prepared by the procedure ofExample 5 and a sample of a cured product was prepared by the method asdescribed in Comparative Example 2. The properties of the curing agentmasterbatch, the curing composition and the cured product are shown inTable 3.

EXAMPLE 9

Three hundred and fifty grams of the dispersion of particles of the 2Mz/EPIKOTE® 828 epoxy adduct prepared by the same procedure as inExample 5 was transferred to a reactor equipped with a heatableagitation device and heated to 60° C. with constant agitation.Subsequently, while maintaining this temperature, 50 g of MR-300poly-MDI was added over a period of about 2 hours. Then, the reactionmixture was heated at the same temperature for additional 4 hours, andthen cooled to form a curing agent masterbatch. This curing agentmasterbatch contained 2.8% of unreacted MR-300 poly-MDI. The viscosityof this curing agent masterbatch at 30° C. was 450,000 cps.Subsequently, a curing composition was prepared by the procedure ofExample 5, and a sample of a cured product was prepared by the methodaccording to Comparative Example 2. The properties of the curing agentmasterbatch, the curing composition and the cured product are shown inTable 3.

EXAMPLE 10

Three hundred and fifty grams of the dispersion of particles of the 2Mz/EPIKOTE® 828 epoxy adduct prepared by the same procedure as inExample 5 was transferred to a reactor equipped with a heatableagitation device. With constant agitation, temperature was brought to60° C. Then, while maintaining this temperature, 100 g of MR-300poly-MDI was added over a period of about 2 hours, and while the sametemperature was maintained, the mixture was heated for additional 4hours, and then cooled to form a curing agent masterbatch. This curingagent masterbatch contained 2.9% of unreacted poly-MDI.

While the trend was the same with other examples, it was observed inthis Example that nearly all the poly-MDI had been consumed in an amountalmost equal to that of the particles in the cured product. Normally,poly-MDI can react only with the hydroxy groups of the additionalproduct, and thus it is believed that such a large amount of poly-MDIwould not be consumed by the addition product alone. Without being heldto a particular theory, it is believed that this level of consumption ispossible only by reaction with the carboxyl groups of the dispersionstabilizer which are immobilized on the particles and the water in theparticles.

The viscosity of this curing agent masterbatch at 30° C. was 1,400,000cps. Subsequently, a curing composition was prepared by the procedure ofExample 5 and a sample of a cured product was prepared by the method asdescribed in Comparative Example 2. The properties of the curing agentmasterbatch, the curing composition and the cured product are shown inTable 3.

As shown in Table 3, the properties of the curing agent masterbatch, thecuring composition and the cured product changed with added amounts ofpoly-MDI. In the instance of the properties of the curing agentmasterbatch, as the added amount of poly-MDI increased, the viscosityincreased and the storage stability extended quickly. From the aspect ofstorage stability, larger amounts of poly-MDI are desirable. However,from the aspect of production, the upper limit is 100 phr., beyond whichthe production will be difficult. Without being held to a particulartheory, various reasons for the increase in viscosity caused byincreased amounts of poly-MDI, include an increase in the concentrationof the dispersed phase. Perhaps, the polymerization of poly-MDI causedby the moisture contained in the dispersion medium, the increase in themolecular weight of the epoxy resin caused by the reaction with a minuteamount of hydroxy groups contained in the epoxy resin used as thedispersion medium, and the increase in viscosity due to thepolymerization of epoxy resin by the adduct, have all contributed.

Like the storage stability of the curing agent masterbatch, the storagestability of the curing composition is improved rapidly by the increaseof the added amount of poly-MDI. Now, the behavior of gel time whichserves as the criterion for the curing rate differs drastically withcuring temperatures. While increase in gel time is only slight in thecuring process at a temperature higher than 120° C. at around 10% ofpoly-MDI, gel time declines gradually with the increase of the amount ofpoly-MDI addition if the amount of addition is increased beyond 10%. Thetrend of this decrease is more significant, the higher the temperatureused for heating. In contrast, in the curing reaction at a temperaturelower than 110° C., the gel time increases with the improvement ofstorage stability. In other words, the curing reactivity declines.

The properties of the cured product vary with the increased amounts ofpoly-MDI added. First, the Tg which is the criterion of heat resistancedeclines, slightly, as increased amounts of poly-MDI are added. Althoughthe tensile strength declines also with increased amounts of poly-MDIadded, the percent elongation increased. Thus the cured product tends tobecome stronger. There is no significant change in the water absorption(criterion of water resistance) with increased amounts of poly-MDIadded.

                                      TABLE 3                                     __________________________________________________________________________                  Comparative                                                                          Example No.                                              Properties    Example 2                                                                            5   6    7    8    9    10                               __________________________________________________________________________    Masterbatch                                                                   Particle size of adduct (μm)                                                             0.21   0.21                                                                              0.21 0.21 0.21 0.21 0.21                             Amount of MR-300 added                                                                      0      10  20   30   40   50   100                              (%/adduct)                                                                    Viscosity (ps. 30° C.)                                                               291    595 1120 1940 3050 4500 14000                            Stable storage period (days)                                                  50° C. ≦1 day                                                                        5   12   14   25   30   54                               30° C. 5      32  61   78   120  260  >360                             Curing composition                                                            Concentration of adduct (%)                                                                 15     15  15   15   15   15   15                               Viscosity (ps, 30° C.)                                                               115    136 167  210  265  351  1070                             Gel time (seconds)                                                            100° C.                                                                              186    467 538  656  818  869  9100                             110° C.                                                                              121    148 160  184  249  398  4600                             120° C.                                                                              65     67  61   50   45   44   15                               140° C.                                                                              30     33  31   30   24   17   5                                Pot life (days)                                                               50° C. ≦1                                                                            11  26   29   48   57   105                              30° C. 10     118 180  230  300  360  >360                             Cured product                                                                 Tg (°C.)                                                                             158    159 158  155  153  151  146                              Tensile properties                                                            Strength (kg/cm.sup.2)                                                                      622    613 591  593  584  582  523                              % Elongation  6      5   8    7    9    13   16                               Water absorption                                                                            0.7    0.9 0.9  0.8  1.0  1.1  1.2                              (%, soaked in boiling                                                         water for 6 hours)                                                            __________________________________________________________________________

EXAMPLE 11

A dispersion of particles of an adduct was prepared by the procedure ofExample 5 except that the particles of the 2 Mz/EPIKOTE® 828 epoxyadduct prepared in Comparative Example 3 were used. The viscosity of thedispersion at 30° C. was 17,700 cps. Three hundred and fifty grams ofthis dispersion were transferred into a reactor equipped with a heatableagitation device, and it was heated to 60° C. with constant agitation.Subsequently, while maintaining this temperature, 10 g of MR-300poly-MDI was added over a period of about one hour and the reactionmixture was heated at the same temperature for additional two hours, andthen cooled to form a curing agent masterbatch. This curing agentmasterbatch contained 2.3% of unreacted poly-MDI. The viscosity of thiscuring agent masterbatch at 30° C. was 37,000 cps. Subsequently, acuring composition was prepared by the procedure of Example 5 and asample of a cured product was prepared by the method as described inComparative Example 5, and a sample of a cured product was prepared bythe method as described in Comparative Example 2. The properties of thecuring agent masterbatch, the curing composition and the cured productare shown in Table 4.

EXAMPLE 12

Three hundred and fifty grams of the dispersion of particles of anadduct prepared by the same procedure as Example 5 was transferred to areactor equipped with a heatable agitation device, and it has heated to60° C. with constant agitation. Subsequently, 20 g Of MR-300 poly-MDIwas added over a period of about one hour at this temperature, and thenthe reaction mixture was heated at the same temperature for additional 2hours, and then cooled to form a curing agent masterbatch. This curingagent masterbatch contained 2.8% of unreacted poly-MDI. The viscosity at30° C. was 72,000 cps. Then, a curing composition was prepared by theprocedure of Example 5, and a sample of a cured product was prepared bythe method as described in Comparative Example 2. The properties of thecuring agent masterbatch, the curing composition and the cured productare shown in Table 4.

EXAMPLE 13

Three hundred and fifty grams of the dispersion of particles of anadduct prepared by the same procedure as Example 5 were transferred to areactor equipped with a heatable agitation device, and was heated to 60°C. with constant agitation. While maintaining this temperature, 30 g ofMR-300 poly-MDI was added over a period of about one hour. Whilemaintaining the same temperature, it was heated for additional 3 hours,and then cooled to form a curing agent masterbatch. This curing agentmasterbatch contained 1.9% of unreacted poly-MDI. The viscosity at 30°C. was 132,000 cps. Subsequently, a curing composition was prepared bythe procedure of Example 5, and a sample of a cured product was preparedby the method described in Comparative Example 2. The properties of thecuring agent masterbatch, the curing composition and the cured productare shown in Table 4.

Comparison of Table 3 with Table 4 clearly shows the effect of the sizeof the particles of the adduct. Although larger particle sizes did notshow a basic difference in the effect of poly-MDI treatment, thesituation is slightly different with smaller particles. With largerparticle sizes, the viscosity declines and the latent effect is greatereven when they were treated by the same amount of poly-MDI. On the otherhand, no significant difference is seen in the properties of the curedproducts.

                  TABLE 4                                                         ______________________________________                                                     Compar-                                                                       ative                                                                         Exam-  Example No.                                               Properties     ple 3    11      12    13                                      ______________________________________                                        Masterbatch                                                                   Particle size of adduct                                                                      0.52     0.52    0.52  0.52                                    (μm)                                                                       Amount of MR-300 added                                                                       0        10      20    30                                      (%/addition product)                                                          Viscosity (ps. 30° C.)                                                                177      370     720   1320                                    Stable storage period                                                         (days)                                                                        50° C.  ≦1 day                                                                          18      35    44                                      30° C.  15       142     161   230                                     Curing composition                                                            Concentration of adduct                                                                      15       15      15    15                                      (%)                                                                           Viscosity (ps, 30° C.)                                                                108      113     142   173                                     Gel time (seconds)                                                            100° C. 192      472     561   726                                     110° C. 132      155     169   225                                     120° C. 68       65      63    51                                      140° C. 30       29      29    28                                      Pot life (days)                                                               50° C.  ≦1                                                                              13      31    42                                      30° C.  22       189     232   320                                     Cured product                                                                 Tg (°C.)                                                                              157      158     155   153                                     Tensile properties                                                            Strength (kg/cm.sup.2)                                                                       618      613     590   586                                     % Elongetion   5        4       6     7                                       Water absorbtion                                                                             0.8      1.0     0.1   0.9                                     (%, soaked in boiling                                                         water for 6 hours)                                                            ______________________________________                                    

EXAMPLE 14

MIBK (2,750 g) was charged in the same reaction apparatus as describedin Comparative Example 3, and then N-methylpiperazine N-MP (195 g) (1.94epoxy equivalent weight) was added, and the temperature was raised to60° C. to dissolve the materials. Then, 425 g of a 30 weight % MIBKsolution of GC-10 dispersion stabilizer, and finally 700 g (1.88 epoxyequivalent weight) of a 50 weight % MIBK solution of EPIKOTE® 828 epoxywas added. They were reacted at 60° C. for 14 hours with agitation at400 r.p.m. to give 174 g of spherical particles of an adduct having aparticle diameter of 0.55 μm, the procedure as described in ComparativeExample 3. The moisture content of the particles of the adduct thusobtained was adjusted to 5.4% by weight, and then the particles weredispersed in DER 332 under the conditions of Example 5 to form adispersion. The viscosity of the dispersion at 30° C. was 16,800 cps.Three hundred and fifty grams of the dispersion were transferred to areactor equipped with a heatable agitation device and heated to 60° C.with constant agitation. Subsequently, while maintaining thistemperature, 15 g of MR-300 poly-MDI was added over a period of aboutone hour, and the mixture was heated for additional 2 hours at the sametemperature, and then cooled to form a curing agent masterbatch. Thiscuring agent masterbatch contained 2.7% of unreacted poly-MDI. Theviscosity of this curing agent masterbatch at 30° C. was 43,000 cps.Then, a curing composition was prepared by the procedure of Example 5,and a sample of a cured product was prepared by the method as describedin Comparative Example 2. The properties are given below.

Curing Agent Masterbatch

Viscosity at 30° C.: 43,000 cps

Stable storage period at 50° C.: 22 days

Curing Composition

Viscosity at 30° C.: 12,100 cps

Stable storage period at 50° C.: 35 DAYS

Gel time at 120° C.: 88 seconds

Properties of Cured Product

Tg: 138° C.

Tensile strength: 586 kg/cm²

% Elongation: 10%

Water absorption after soaking in boiling water for 6 hours: 1.1%

COMPARATIVE EXAMPLE 4

The pulverized particles of the adduct (200 g) as prepared inComparative Example 1 was added to nearly OH-free BADGE (herein "DER332", a product of Dow Chemical Company, epoxy equivalent weight: 173)(300 g). Then the mixture was briefly blended and was passed through athree-roll mill three times to completely disperse the particles inBADGE epoxy. The dispersion 250 g was transferred into a reactorequipped with a heatable agitation device and heated to 60° C. withconstant agitation. While maintaining this temperature, MILLIONATEMR-300 methylene diphenyl diisocyanate/formaldehyde condensate 4 g(herein "poly-MDI"), a product of Nippon Polyurethane Kogyo K.K. wasadded over a period of about one hour. The mixture was heated foradditional 2 hours at the same temperature and then cooled to prepare acuring agent masterbatch. According to the result of analysis byShimadzu Seisakusho's FTIR analyzer, unreacted poly-MDI was not detectedin the reaction mixture. The properties of the curing agent masterbatchthus prepared are shown in Table 5. The initial viscosity was measuredby a Brookfield viscosimeter, and the stable storage period is the timeuntil gelation takes place.

In order to measure the properties of the curing agent masterbatch, thecuring agent masterbatch was added to EPIKOTE® 828 epoxy to prepare acuring composition. The amount added was sufficient to obtain a curingcomposition having 10% by weight adduct based on the total weight of theepoxy. The initial viscosity, the gel time (measured by stroke curetechnique) as the criterion of curing rate and the stable storage periodof this curing composition were measured and the results are shown inTable 5. A portion of the curing composition was heated and cured at100° C. for one hour and then at 150° C. for 3 hours to form a curedarticle, and its glass transition temperature (Tg), tensile propertiesand water absorption were measured. The methods of measurements employedare as follows:

Tg: by a differential thermal analyzer

Tensile properties: procedures specified in JIS K-7113

For water absorption, a sample (39 mm in diameter and 5 mm in thickness)was soaked in water at 100° C. for 6 hours, and the increase in weightwas measured. The results are shogun in Table 5.

COMPARATIVE EXAMPLE 5

The 2 Mz/EPIKOTE® 828 epoxy adduct prepared in the same manner asComparative Example 4 was crushed and pulverized in a jet mill to obtainparticles having a Stokes diameter of 9.8 μm. These particles wereprocessed in the same manner as in Comparative Example 4 to form a DER®332 epoxy masterbatch. Only the amount of the poly-MDI used fortreatment was different. It was 2% by weight based on the weight of theparticles of the adduct. The properties of this curing agentmasterbatch, the curing composition prepared in the same manner as inComparative Example 4 and the cured article are shown in Table 5.

EXAMPLE 15

MIBK (2,805 g) was charged in a 5,000 ml three-necked round bottom flaskequipped with a thermometer, a reflux condenser and a glass halfmoon-shaped agitation device. 2 Mz (150 g), a RESEDA GP-300styrene/glycidyl methacrylate copolymer grafted with methylmethacrylate, a product of Toagosei Chemical Ind. Co., Ltd. (24.3) g asa dispersion stabilizer, and 150.5 g of a 32.3% MIBK solution of RESEDAGP-101S methyl methacrylate/methacrylic acid copolymergraft-copolymerized with methyl methacrylate, a product of ToagoseiChemical Ind. Co., Ltd. as a dispersion stabilizer were added, and thenthe temperature was raised to 70° C. to dissolve these substancescompletely. Then, 672.9 g of a 50 weight % solution of EPIKOTE® 828epoxy was added, and the reaction was carried out at 70° C. for 9 hours,while the contents were agitated at the rate of 400 r.p.m. The reactionmixture which was faintly milky at the beginning changed gradually intoa milky white, opaque with the progress of reaction, and it became acream-colored milky white liquid at the end of the reaction.

When the conversion attained 100% by the reaction carried out at 70° C.for 9 hours, the reaction mixture was cooled down to room temperature,and dried by a GS-31 spray dryer for organic solvent system,manufactured by Yamato Kagaku K.K. Dried particles of a curing agentwere recovered. The following conditions were employed in spray-dryingthe particles.

    ______________________________________                                        Spray nozzle diameter  0.4 mm                                                 Temperature at the entrance                                                                          110° C.                                         of drying chamber                                                             Temperature at the exit                                                                              75° C.                                          from drying chamber                                                           Flow rate of hot gas   0.53 m.sup.3 /min.                                     Spray pressure         1.0 kg/cm.sup.2                                        Fluid transport rate   7.9 g/min.                                             Temperature at the     12° C.                                          exit from condenser                                                           ______________________________________                                    

A near theoretical amount of dried particles was recovered by spraydrying. The average particle diameter of the particles of the curingagent was measured by the method described in Comparative Example 1. Itwas 1.1 μm. The ratio of MIBK recovered was 98.8%. When this MIBK wassubjected to analysis, none of the starting materials were detected.

Two hundred grams of the particles of the adduct thus prepared wereadded to 300 g of DER® 332 epoxy, briefly kneaded and completelydispersed by passing through a three-roll mill. In the case of thepulverized particles of the adduct of Comparative Examples 4 and 5,three passages through the roll mill were required for obtaining aperfect dispersion. In contrast, in the case of the spherical particlesof the adduct of this Example, a perfect dispersed state was reached bya single passage. Two hundred and fifty grams of the dispersion weretransferred to a reactor equipped with a heatable agitation device andheated to 60° C. with constant agitation. While maintaining thistemperature, MILLIONATE MR-300 methylene diphenyl diisocyanate(MDI)/formaldehyde condensate 15 g, a product of Nippon PolyurethaneK.K. was added over a period of about one hour, and the mixture washeated for 6 hours to completely react the poly-MDI added. Theproperties of this curing agent masterbatch are shown in Table 5.

The curing agent masterbatch thus prepared was added to EPIKOTE® 828epoxy so that the amount would be 10 p.h.r., based on the weight of theadduct, to prepare a curing composition. The properties of the curingcomposition and the cured article were measured in the same manner asComparative Example 4. The results are shown in Table 5.

EXAMPLE 16

MIBK (3,390 g) was charged into a 5,000 ml three-necked round bottomflask equipped with a thermometer, a reflux condenser and a glass halfmoon-shaped agitation device.-After adding 2 Mz (140 g) and RESEDAGP-300 copolymer (22.7 g) as the dispersion stabilizer, the temperaturewas raised to 70° C. to completely dissolve the mixture. Then, 628 g ofa 50 weight % MIBK solution of EPIKOTE® 828 epoxy was added. While thecontents were agitated at a rate of 400 r.p.m., the reaction was carriedout at 70° C. for 9 hours to bring the conversion to 100%. Thedispersion of the adduct thus prepared was spray-dried under the sameconditions as in Example 15 to obtain dried particles. The averageparticle diameter of the spherical particles thus obtained was 2.8 μm.FIG. 5 is an electron micrograph showing the morphology of theparticles.

Two hundred grams of the particles of the adduct were dispersed in 300 gof DER 332 epoxy by the procedure of Example 15, and 250 g of thedispersion thus prepared was transferred to the reactor equipped with aheatable agitation device and heated to 60° C. with constant agitation.While maintaining this temperature, 4 g of MILLIONATE MR-300 poly-MDIwas added over a period of about one hour and the mixture was agitatedand heated for 4 hours while maintaining the same temperature to reactall the added poly-MDI. The properties of the curing agent masterbatchthus obtained are shown in Table 5.

By the procedure of Example 15, 10 phr. of the curing agent masterbatchwas added to EPIKOTE 828 epoxy to prepare a curing composition, and theproperties of the curing composition and the cured article weremeasured. The results are shown in Table 5.

EXAMPLE 17

MIBK (2,805 g) was charged on a 5,000 ml three-necked round bottom flaskequipped with a thermometer, a reflux condenser and a glass halfmoon-shaped agitation device. 2 Mz (150 g), RESEDA GP-300 copolymer(24,3 g), and RESEDA GP-102S copolymer from Toagosei Chemical Ind. Co.,Ltd. (153.8 g) were added to the flask, and the temperature was raisedto 70° C. to completely dissolve these substances. Subsequently, 673 gof a 50 weight % solution of EPIKOTE® 828 was added, and while thecontents were agitated at a rate of 250 rpm, the reaction was carriedout at 70° C. for 9 hours to bring the conversion to 100%. Thedispersion of the adduct thus prepared was spray-dried under the sameconditions as in Example 15 to obtain dried particles. The averageparticle diameter was 9.9 μm.

Two hundred grams of the particles of the adduct were dispersed in 300 gof DER® 332 epoxy by the procedure of Example 15 and 250 g of thedispersion thus obtained was transferred to a reactor equipped with aheatable agitation device and heated to 60° C. with constant agitation.While maintaining this temperature, MILLIONATE® MR-300 poly-MDI (2 g)was added over a period of about one hour, and while keeping at the sametemperature, the mixture was agitated and heated for 4 hours to reactall the added poly-MDI. The properties of the curing agent masterbatchare shown in Table 5.

Ten phr. of the curing agent masterbatch was added to EPIKOTE 828 epoxyby the procedure of Example 15 to prepare a curing composition, and theproperties of this curing agent composition and the cured articles weremeasured and the results are shown in Table 5.

EXAMPLE 18

MIBK (2,352 g) was charged in a 5000 ml three-necked round bottom flaskequipped with a thermometer, a reflux condenser and a glass halfmoon-shaped agitation device. After adding N-MP (190.4 g) and RESEDAGP-300 copolymer (27 g) to the reactor, the temperature was raised to70° C. to dissolve these substances. Then, 700 g of a 50 weight % MIBKsolution of EPIKOTE® 828 epoxy was added. With constant agitation at arate of 250 rpm, the contents were reacted at 70° C. for 20 hours tobring the conversion to 100° C. The dispersion of the adduct thusprepared was spray-dried under the same conditions as in Example 15 toobtain dried spherical particles. The average particle diameter was 2.7μm.

Two hundred grams of the particles of the adduct was dispersed in 300 gof DER® 332 epoxy by the procedure of Example 15 and two hundred andfifty grams of the dispersion thus obtained was transferred to a reactorequipped with a heatable agitation device and heated to 60° C. withagitation. While maintaining this temperature, MILLIONATE® MR-300poly-MDI (4 g) was added over a period of about one hour. Whilemaintaining the same temperature, the mixture was agitated and heatedfor 4 hours to completely react the added poly-MDI. The properties ofthe curing agent masterbatch are shown in Table 5.

Ten phr. of the curing agent masterbatch was added to EPIKOTE 828 epoxyby the procedure of Example 15 to prepare a curing composition, and theproperties of the curing composition and the cured article were measuredand the results are shown in Table 5.

The curing agent masterbatch derived from the fine spherical particle ofthe adduct prepared by the precipitation method of this invention, thoseprepared by the pulverizing method of the prior art, the curingcomposition added with such curing agent masterbatches, and the curedarticles are compared in Table 5 for their properties. In this case, theparticle size is varied over a wide range, since the particle size cansignificantly affect the viscosity and the curability. The results shownin Table 5 indicate the following:

(1) The spherical particles of the adduct of this invention and thepulverized particles of the adduct prepared by the method of the priorart have nearly identical curability (based on gel time) and storagestability properties as a result of the treatment with thepolyfunctional isocyanate compound under the same conditions, if theparticle size of the adduct is kept the same.

(2) If the particle size of the adduct differs, smaller particle sizeswill give a better curability, but the viscosity of the curing agentmasterbatch and the curing composition will increase.

(3) Smaller sizes of the adduct will give a cured article with slightlybetter properties. However, there is hardly any difference due to themorphology of the particle of the adduct.

When the particles of the adduct obtained by the method of the prior artare compared with those of the adduct of the present invention, thepresent invention, as the curing agent masterbatch and the curingcomposition, is superior to the prior art in the following aspects.

(1) In the preparation of a curing agent masterbatch, the dispersion inthe epoxy resin as the dispersion medium is easier to take place. Whilethree passages are required for obtaining a complete dispersion of theparticles of the adduct by the method of the prior art, only a singlepassage can achieve a perfect dispersion for the particles of the adductof the present invention.

(2) If comparison is made with the approximately same particle size ofthe particles of the adducts, the particles of the adducts, by thepresent invention has a far lower viscosity of the curing agentmasterbatch.

(3) If a comparison is made between prior art particles of thisinvention wherein the particles of each have approximately the sameparticle size, the particles of the invention result in a curingcomposition having a far lower viscosity.

                                      TABLE 5                                     __________________________________________________________________________                 Comparative Example No.                                                                      Example No.                                       Properties   4       5      15  16  17   18                                   __________________________________________________________________________    Masterbatch                                                                   Composition of adduct                                                                      2Mz/    "      "   "   "    N-MP/                                             Epikote 828                 Epikote 828                          Shape of particle                                                                          Pulverized                                                                            Pulverized                                                                           Sphere                                                                            Sphere                                                                            Sphere                                                                             Sphere                               Particle size (μm)                                                                      2.9     9.8    1.1 2.8 9.9  2.7                                  No. of passage through                                                                     3       3      1   1   1    1                                    the three-roll mill                                                           required for dispersion                                                       Viscosity (1000 cps, 20° C.)                                                        584     425    283 231 188  226                                  Stable storage period                                                                      350     Longer than                                                                          240 350 Longer                                                                             Longer                               (days, at 20° C.)                                                                           360            than 360                                                                           than 360                             Curing composition                                                            Viscosity (1000 cps. 20° C.)                                                        56      48     35  24  20   23                                   Gel time (seconds)                                                            120° C.                                                                             111     124    99  104 114  138                                  140° C.                                                                             55      63     50  53  56   84                                   Pot life     168     Longer than                                                                          217 175 Longer                                                                             Longer                               (days, at 20° than 360       than 360                                                                           than 360                             Cured article                                                                 Appearance   Reddish brown                                                                         "      "   "   "    Pale yellow                                       Translucent                 Clear                                Tg (°C.)                                                                            152     150    158 153 151  145                                  Tensile properties                                                            Strength (kg/cm.sup.2)                                                                     522     532    570 526 541  508                                  % Elongation 2.3     3.1    5.8 3.6 2.4  8.8                                  Water absorption                                                                           0.8     0.9    0.7 0.7 0.8  0.8                                  (%, after soaking in                                                          boiling water for 6 hours)                                                    __________________________________________________________________________

What is claimed is:
 1. A curing agent for epoxy resin which is finesubstantially spherical particles of an amine compound having only oneactive amino-hydrogen/polyfunctional epoxy compound adduct wherein thesize of said particles is in the range or 0.1 μm to 30 μm, saidparticles being obtained by reacting an amine compound having only oneactive amino-hydrogen and a polyfunctional epoxy compound at a ratio ofthe epoxy group in said epoxy compound to the active amino-hydrogen insaid amine compound of substantially 1:1 in the presence of a dispersionstabilizer in an organic solvent capable of dissolving both said aminecompound and said epoxy compound but incapable of dissolving the adductformed therefrom at elevated temperatures with agitation, saiddispersion stabilizer being a polymeric compound having high affinity toboth said organic solvent and said adduct formed.
 2. The curing agent ofclaim 1 having a melting point of at least 50° C.
 3. The curing agent ofclaim 1, wherein said amine compound is 2-methylimidazole.
 4. The curingagent of claim 1, wherein said amine compound is N-methylpiperazine. 5.The curing agent of claim 1, wherein said epoxy compound has an epoxyequivalent weight of at most 1,000.
 6. The curing agent of claim 5,wherein said epoxy compound has an epoxy equivalent weight of at most500.
 7. The curing agent of claim 6, wherein said epoxy compound isbisphenol A diglycidyl ether.
 8. The curing agent of claim 1, whereinsaid dispersion stabilizer has a molecular weight of 1,000 to 300,000.9. The curing agent of claim 8, wherein said dispersion stabilizer is amethyl methacrylate/methacrylic acid copolymer graft-copolymerized withmethyl methacrylate or a styrene/glycidyl methacrylate copolymergraft-copolymerized with methyl methacrylate.
 10. The curing agent ofclaim 1, wherein said organic solvent has a solubility parameter of 8 to11.
 11. The curing agent of claim 10, wherein said organic solvent ismethyl isobutyl ketone or xylene.
 12. The curing agent of claim 1,wherein said elevated temperatures are 40° C. to 90° C.